“Ludwig clearly implied that an increase in water use or farming productivity would lead to an increase in Australia's population.”

No I didn’t.

Increasing primary produce will serve to facilitate increased populations, generally speaking, with a global perspective, as it has done since the dawn of agriculture. But in Australia it won’t, because we already have high population growth, due mostly to high immigration, which is largely [not entirely] independent of domestic food production. Food production in this country is much greater than that needed to feed our population, as Perseus points out.

Increased productivity in Australia is all about export income, broadly speaking. This will contribute to an ever-growing economy, but rather than this leading to an improvement in standard of living / quality of life for Australians, we will simply be continuing to play catch-up in trying to provide the same economic benefits for ever-more people.

Perversely, as our economic growth becomes stronger, there is a push for higher immigration. So to that end, there is some relationship in Australia between better water-use efficiency with agriculture and population growth, but it is not a strong correlation.

I thank Perseus for a reasonably good posting, containing material worthy of careful consideration in this debate…. and no deliberately offensive comments!! [?blog stalking?] I hope he can see that we do actually share a fair bit of common ground here.

I don't want to say too much at the moment except encourage other contributors to continue their excellent contributions.
One of the interesting things I found in irrigation science was that the previous generation of irrigation experts realised that old concepts of "irrigation efficiency" didn't always measure overall water efficiencies well. Some of the "lost" water was not actually lost to useful farming. The green water concept rightly added insights that captured some of this "lost water" (but not really lost) as conceptually useful flows.
Recycling concepts mentioned by Perseus,KAEP add other fresh concepts and I'm very pleased to see them appear hear. Clearly deep percolation and other rainfall losses to ochre flows are real losses and can have bad side effects like salinity. The idea of recycling "ochre" flows to the atmosphere seems very interesting and it would be good to know what atmospheric modelling has to say about their quantitative effect on rainfall. Switching urban development away from Sydney or at least upstream in catchments is another intriguing idea in this context .
It would also be interesting to explore how all of this discussion relates to Andrew Frazer's (spelling,name correct?) fascinating activities as expounded on TV Australian Story recently.

As far as my response to Ludvig's extra questions, I'm a bit unsure of what Ludvig is getting at and whether it fits the theme.

No wonder our water courses scream out in agony.(Murray - Darling) When one square metre of growing cotton consumes 700 litres of water to attain harvest then that to me is obscene!

Add to this equation the run off from pesticides, growth promoters and such and the production of this textile does not seem so environmentally friendly in the overall context.(Blue-Green Algae)

The Nimbin crowd may be "off the planet" more often than not, but suggestions from their camp that Hemp ( a relation to Indian Hemp) be harvested as a textile is not being seriously looked at. It consumes less than a third of the water needed to produce the same amount of cotton fibre.

The 'Trash' that is left after harvest can also be useful in re-nitrogenising the soils.

The governments' collective response: " WE can't do that! [It] is hemp and could be used for illicit purposes...!"

No lateral thinkers, no one prepared to do an honest days research, but many nay sayers of Doom and Collected Gloom, say we need to post- haste dam all the NT rivers and pipe the water down south.

Oh dear, haven't we learned anything from the past 215 years?

The role of cycling in the contribution value of water serves to focus on the wisdom behind the diversion of water back into the snowy river. It may well have been necessary to restore flow to that river but it does not follow that the water must then be wasted by flowing into the sea. It was the river itself that needed restoring but the water should then be captured near the mouth and diverted to additional economic and ecological uses.

Is it within pumping distance to Melbourne? The experience of California, with water for LA pumped from the high rainfall north of the state, and over a 1000m mountain range, suggest it would be viable.

Other options would be to overlap supply. That is, if there is a power station between the Snowy mouth and Melbourne then use the snowy water in the power station and divert the station's existing water allocation to Melbourne. Then add sewrage nutrients to the water as it passes through humans and pump it up to the irrigation areas for further cycling. This classic multiple use of the one water body would end up producing the same amount of crops, or even more, as it did prior to its removal from the Murray catchment.

It really is a fascinating place outside the square, don't you think?

David, I don’t get it.

I would have thought these two points are self-explanatory and highly relevant

Dealing with the first one: Being prepared for drought is essential. Or put a different way; dealing with Australia’s erratic rainfall, which appears to be lower in recent years in many places, is an essential part of the planning process for improving productivity. We simply MUST have a system that will see us through the downturns.

It is true that if we are close to maximum efficiency with water usage in the good times, we are in trouble in the bad times, unless we have built in a backup mechanism whereby we set aside a good part of our water resource which can be tapped into in dry times, or we set aside a good part of the profits to get us by when (not if) the crops fail.

I really worry that improvements in water-usage efficiency will simply lead to much bigger heartache for more people and more Perseus-style chronic disillusionment with the authorities when the rains don’t come.

Albie, your concern about the 700 litres/m2 used by cotton is the product of the political green/left exploiting your lack of knowledge. For the record, my wet schlerophyl forest uses 1700 litres per m2 each year but could use up to 2500 litres, my mangos and macadamias use 2300 litres/m2 and a rainforest could use up to 3000 litres/m2.

More telling is the fact that most cotton is grown in the 500 to 600mm rainfall zone and, lest the maths might boggle your suburban mind, that equates to 500 to 600 litres per square metre. And if the cotton was not being grown on the site then the original forested grassland would still have used 500 to 600 litres/m2. So the additional use of water by the cotton crop is only 100 to 200 litres/m2. Less in a good year and more in a bad one.

Furthermore, most of the extra water that is used by the cotton industry is merely the re-capture of part of the extra runoff that was produced by clearing in the upper catchment.

And Ludwig, how can your suggestion, that "improvements in water-usage efficiency will simply lead to much bigger heartache for more people" be interpreted as anything but, Luddite pessimism? So we'll all just sit here doing continual revisions of Beattie's "missprint for the bush", will we?

David, it is pretty clear we'll get more work done on this topic on another forum. See you there.